When kneading kneading materials that include raw rubber and carbon black in a closed-type rubber kneader, the extent of the kneading efficiency of the closed-type rubber kneader is evaluated in accordance with the magnitude of the evaluation index calculated from unit work/total amount of shear by calculating an evaluation index calculated by a calculation device based on a total amount of shear obtained by integrating the shear velocity applied to the kneading materials by a rotor that is being driven to rotate by the rotor drive unit of the kneader over the kneading time, and a unit work obtained by dividing the integrated power obtained by integrating the instantaneous power of the rotor drive unit over the kneading time by the mass of the kneading materials.